Plates suitable as noise protection elements made of basically frangible acrylic glass in which plastic monofilament threads are embedded to reduce splintering in the possible event of breakage of the glass.
Plates of the prior art which are secured against the origination and falling down of loose fragments are known from EP 0 407 852. The plates disclosed therein contain, embedded therein, relative to the plate cross-section substantially essentially centrally located monofilament synthetic threads, or a web of such threads. Monofilament threads made of polyamide are particularly suitable as synthetic threads. In the above-mentioned EP 0 407 852 it is emphasized that the embedded synthetic threads are substantially invisible, so that the elements remain transparent. Furthermore, because the synthetic threads are embedded into the interior of the plate an optimal protection against weathering is provided. The cleaning of the plate is unproblematic. Furthermore, even at low temperatures, i.e below xe2x88x9220xc2x0 C., they are still secured against the occurrence and dropping of loose fragments. Nevertheless, it must be stressed that the central location substantially increases the production cost of such plates.
In accordance with EP 0 826 832 break resistant noise protection plates of acrylic polymers are known which contain synthetic filaments wherein the filaments are not centrally located. Rather the filaments are located in a spacing of between 20 and 35% of the total thickness of the plate relative to their surface with respect to that surface which is exposed in a possible crash. In accordance with the disclosure of EP 0 826 832 it is, also possible to obtain breakage secured noise protecting elements even with the non-central location. However, it remains to be determined whether the test methods utilized to substantiate this alleged effect are sufficient, since the utilized impact energies lie in an insufficiently high area. In contrast thereto, an element in accordance with EP 0 407 852 withstands a test under din 52 250, that is to say, a corresponding plate which is free on both sides is shattered by a steel ball of mass 4.1 kilograms dropped from a height of 9 meters, but nevertheless, produces no free fragments. It is especially to be noted that all thus originating fragments are held together by the embedded threads.
In accordance with the present invention, it has been unexpectedly and surprisingly found that it is possible to obtain shatter protection and noise protection by means of plates of the prior art wherein at least one of the embedded threads has a maximum deviation of 1 mm or more from a straight line drawn between the ends of these plates.
This, so to speak sagging xe2x80x9cpositioningxe2x80x9d of the threads in the acrylic glass matrix leads, under certain circumstances, to an advantageous behavior of the plates of the present invention utilized as sound protection walls in the appropriate tests. For example, in accordance with ZTV-LSW 88 under 3.4.2 and under the guideline LS3 of the German Federal Ministry for Traffic xe2x80x9cAdditional technical rules and guidelines for the implementation of sound protection walls on streetsxe2x80x9d. The term xe2x80x9cmaximum deviationxe2x80x9d in sense of the invention is the largest spacing of the threads from the theoretical line drawn between the ends of said threads. In the preferred embodiment it is provided that this maximum deviation is 3 mm or more. It is even more desirable if the maximum deviation in accordance with the plate of the present invention is 5 mm or more.
This maximum deviation however, must not lead thereto that the threads lie outside the plate, rather it must always be guaranteed in the scope of the invention that the synthetic threads are actually embedded. The maximum deviation which can also be more simply described as the bending of the synthetic threads can, therefore, never be greater than the plate thickness less the thread diameter.
The deviation of the synthetic threads in accordance with the present invention can be perpendicular to the plane of the plate. Such an orientation of the embedded threads can be achieved thereby that the threads are embedded under the influence of gravity after the acrylic glass forming mass is poured in a xe2x80x9clying chamberxe2x80x9d procedure.
Alternatively to this procedure, there is another preferred embodiment wherein the deviation of the plastic threads is substantially parallel to the thread plane. Such an arrangement of the thread orientation is readily given thereby that the plate is poured in the so called Rostero procedure. In substantially vertically standing chambers as is common in this procedure, the threads bend or hang under the influence of gravity parallel to the plane of the plate.
Yet another useful procedure for preparing the plates in accordance with the present invention is one wherein the threads sag substantially perpendicular to the plate plane and the plate contains the threads whose deviation is substantially parallel to the thread plane. Such an arrangement of the securing threads is obtained thereby wherein two threads of different lengths are utilized and thus, one of the threads is substantially parallel to the glass surface and the other thread has a deviation relative to the plate plane.
It is also possible to glue together a pair of 15 mm plates with vertical or parallel deviation to the surface to provide a 30 mm plate and thus, to obtain one within the scope of the present invention.
A particular case exists when rolled embedded polyamide threads are utilized. These give rise to a particularly useful breaking behavior. It is meaningful to utilize transparent polyamide threads, since otherwise the transparency of the plate is sharply reduced.
According to the selected procedure and production of the plates in accordance with the present invention it is thus possible to provide virtually any desired orientation of the synthetic threads in the polymer matrix.
Thus, next to a perpendicular or parallel arrangement relative to the plate plane it is also possible to achieve a deviation which lies in a free gradation between these two limit values.
In accordance with the present invention, the threads can run substantially perpendicular to a surface of a plate.
Furthermore, this invention makes it possible to embed threads in the polymer matrix which do not run parallel to a surface but, for example, are embedded transverse thereto.
This means with a view to the first variant, in a particularly desirable embodiment each of the thread ends of at least one thread subtend substantially the same separation from a surface of the thread plane and/or to one of the edges of the plate. With respect to the previously specified condition, the threads are embedded substantially parallel to a surface of the plate plane and/or to one of the edges of the plate.
Alternatively with respect to the second variant there are also preferred embodiments wherein the distance of the thread ends of at least one thread to a surface in the plate plane and/or an edge of the plate are different. Particularly from the last named circumstance it follows that the creation of a sound barrier element in accordance with the present invention, is substantially simpler relative to the formation of an element in accordance with the state of art, since substantially higher tolerances may be taken into account, in fact may be desired without suffering any disadvantages with respect to a breakage condition.
Basically seen the embedded synthetic threads can be so oriented that they are parallel to each other in only one direction, or so that they run parallel to each other in two or more directions. Herein in the last named case, it is possible among other things that the two directions form a mutual angle of 90xc2x0 or also an angle of less than 90xc2x0.
As plastic threads, monofilament threads of polyamide or polypropylene are particularly suitable because of their adhesibility to the surrounding acrylic glass is relatively small and therefore at substantially reduced temperature there is no noticeable loss in the tear resistance. At the breaking of the acrylic glass, the monofilament synthetic threads can stretch and therefore, do not rip or in any event do so minimally and therefore hold the thus produced fragments together. The diameter of the monofilament threads may usefully lie between 0.2 and 2 mm. The sidewards distance between neighboring threads can lie between 8 and 100 mm. However, separations greater or less than this are possible.
In addition, at least a part of the threads or if desired all of the threads, may be colored to give contrast. For example, this coloring may be black for the formation of the sound protecting elements this always serves to protect the elements from birds.
Plates in accordance with the invention are made with acrylic glass and can be produced by one skilled in the art from generally speaking known materials. Thus, preferably the plates are poured from methylmethacrylate syrup. The size of the plates varies in the range of 1 m by 2 m to 2 m by 3 m, or even larger. The thickness of the plates lies in the range of 5 to 30 mm, suitably 12 to 25 mm, most desirably 15 to 20 mm. The plates in accordance with the present invention may be characterized by a series of particularly advantageous properties.
The plates in accordance with the present invention show very good splinter binding properties in particular, at higher destruction spends or lower temperatures. It is particularly advantageous to provide a deviation of the threads of more than 3 mm, a displacement arrangement of the thread ends or a double layered arrangement of the polyamide threads, or a net type hang through arrangement of the safety threads.
The thus described plates are especially suitable for use as sound protection plates in the railroad or rapid transit area, since here particularly high destruction speeds can occur. A further advantage of the plates of the present invention resides therein with one sided installation. The strongly sagging bi-layered or sagging networks exhibit an excellent cohesion in contrast to centrally centered polyamide threads oriented parallel to the surface of the plate. In accordance with the present invention, the present invention may be illustrated by means of the drawings as follows: